Current ways of nutting out when a person died aren't exact, especially in the first 24 hours after death.

Getty Images: Kirk Marsh

Genetic clocks that start ticking after you die could one day help forensic investigators better nail down time of death.

Key points

Key points:

After a person dies, cells ramp up or slow down gene activity

An international team analysed gene activity in 36 different body tissues at different time intervals after death

They found patterns which, when combined with software, could be used to help determine time of death

Before it's used by forensic investigators, the software needs fine-tuning

When our heart stops beating, our body tissues don't instantly up and die too. The genetic machinery inside some cells can keep whirring away hours — perhaps even a couple of days — after we've shuffled off this mortal coil.

Researchers from Europe and the Americas have found certain genes ramp up or wind down in skin, lungs and other body tissues in the hours after death.

They also developed software that can analyse these gene patterns to calculate how long since that person died.

What happens to genes after death?

Roderic Guigó, at the Centre for Genomic Regulation in Spain, and an international team decided to investigate how death and the hours afterwards affect gene activity.

Their aim was to create the first comprehensive map of gene activity after death.

"Most of what we know about gene expression in tissues has been investigated through the analysis of samples taken from dead people," said computational biologist Professor Guigó.

The team analysed data from the US-based Genotype-Tissue Expression (GTEx) project. The GTEx repository contains thousands of tissue samples collected from corpses at different time intervals after death, along with their gene activity.

Forensic scientists currently establish a window of time of death in a range of ways, each of which "aims to narrow that window", said Brendan Chapman, a forensic biologist at Murdoch University in Perth.

These include taking a body's deep internal temperature, measuring the stiffness of muscles (rigor mortis), electrically stimulating face muscles to measure excitability, potassium levels in eyeball fluid and taking stock of maggots and other creepy-crawlies.

"Body temperature, for instance, gives you a window of plus or minus 2.8 hours — at best," Mr Chapman said.

So the new gene-activity analysis, Mr Chapman said, is "a brilliant foundation" to help investigators calculate time of death, particularly within the first 24 hours.

The major hiccup was sample quality.

"These are clinically collected samples, collected for various other purposes in a clinical environment and well-preserved, " he said.

"It's not like someone's house in the middle of summer, or out in the bush. What effect that has is unknown."

And in Australia, that's a problem.

"Tissue is likely to degrade very quickly, providing a very short window of opportunity to use the gene-expression method to predict [time of death]," Griffith University forensic biologist Kirsty Wright said.

Before the software is added to the forensic toolkit, Professor Guigó said, it does need some additional fine-tuning to take these factors into account.